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Journal of Environmental Management 211 (2018) 256e268

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Journal of Environmental Management

journal homepage: www.elsevier .com/locate/ jenvman

Research article

Biochar feedstock and pyrolysis temperature effects on leachate: DOCcharacteristics and nitrate losses from a Brazilian Cerrado Arenosolmixed with agricultural waste biochars

Alicia B. Speratti a, *, Mark S. Johnson a, b, Heiriane Martins Sousa c, Higo J. Dalmagro d,Eduardo Guimar~aes Couto e

a Institute for Resources, Environment and Sustainability, University of British Columbia, 2202 Main Mall, Vancouver, British Columbia, V6T 1Z4, Canadab Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, BC, Canadac Programa de P�os-Graduaç~ao em Agricultura Tropical, Faculdade de Agronomia e Zootecnia, Universidade Federal de Mato Grosso (UFMT), Cuiab�a, MatoGrosso, 78060-900, Brazild Programa de P�os-Graduaç~ao em Ciencias Ambiental, Universidade de Cuiab�a (UNIC), Cuiab�a, Mato Grosso, 78065-900, Brazile Departamento de Solos e Engenharia Rural, Faculdade de Agronomia e Zootecnia, Universidade Federal de Mato Grosso, Cuiab�a, Mato Grosso, 78060-900,Brazil

a r t i c l e i n f o

Article history:Received 10 September 2017Received in revised form18 December 2017Accepted 19 December 2017Available online 4 February 2018

Keywords:BiocharAgricultural wasteDissolved organic carbonNitrateFluorescence spectroscopyPARAFAC

* Corresponding author.E-mail addresses: alisperat@gmail.com (A.B. Spe

(M.S. Johnson), heirianemartins@hotmail.com (H.M. Scom (H.J. Dalmagro), couto@ufmt.br (E.G. Couto).

https://doi.org/10.1016/j.jenvman.2017.12.0520301-4797/© 2018 Elsevier Ltd. All rights reserved.

a b s t r a c t

Dissolved organic carbon (DOC) leached from Brazilian Cerrado Arenosols can lead to carbon (C) lossesand lower soil fertility, while excessive nutrient, e.g. nitrate (NO3

�), leaching can potentially cause watercontamination. As biochar has been shown to stabilize C and retain soil nutrients, a greenhouseexperiment was conducted to test different biochars’ contributions to DOC and NO3

� leaching from asandy soil. Biochars were made from four local agricultural waste feedstocks (cotton residue, swinemanure, eucalyptus sawmill residue, sugarcane filtercake) pyrolysed at 400, 500 and 600 �C. Biochar wasmixed with soil at 5% weight in pots and maize seeds planted. Leachate was collected weekly for sixweeks and analyzed for DOC and NO3

� concentrations, while fluorescence spectroscopy with parallelfactor analysis (PARAFAC) was used to interpret DOC characteristics. Cotton and swine manure biochartreatments had higher DOC and NO3

� losses than eucalyptus biochar, filtercake biochar, and controltreatments. Cotton and swine manure biochar treatments at high temperatures lost mostly terrestrial,humified DOC, while swine manure, filtercake, and eucalyptus biochars at low temperatures lost mostlylabile, microbially-derived DOC. Through the practical use of fluorescence spectroscopy, our studyidentified filtercake and eucalyptus biochars as most promising for retaining DOC and NO3

� in a CerradoArenosol, potentially reducing stable C and nutrient losses.

© 2018 Elsevier Ltd. All rights reserved.

1. Introduction

Arenosols (sandy soils) account for 13% of the area of the state ofMato Grosso, Brazil, (about 11.7 million ha), and their use as culti-vated soils is increasing, particularly for growing maize (SEPLAN,2008). However, Arenosols are low in organic matter, and theirhigh sand content causes lowwater retention (da Costa et al., 2013).Carbon (C) in the form of dissolved organic carbon (DOC) and

ratti), mark.johnson@ubc.caousa), higojdalmagro@gmail.

nutrients, such as nitrogen (N) in the form of nitrate (NO3�), are

easily leached from these soils. As their use for agriculture (inparticular crops such as soybean and maize) is of increasingimportance to the economy of Mato Grosso, sustainable manage-ment practices such as adding organic matter are necessary toimprove the Arenosol's physico-chemical properties. Among thevarious types of organic amendments that can be added to soil,biochar is one that is considered efficient and stable in the long-term (Clough and Condron, 2010; Lehmann, 2007). Biochar refersto charcoal derived from waste biomass by pyrolysis, which hasbeen shown to improve fertility, carbon sequestration, and water-holding capacity in soils (Lehmann and Joseph, 2009). Its poten-tial use in strategies for improving the agronomic performance of

A.B. Speratti et al. / Journal of Environmental Management 211 (2018) 256e268 257

sandy soils in Mato Grosso could thus be beneficial, as observed inother tropical soils (Jeffery et al., 2017). Less is known, however,about the effects of biochar use in tropical Arenosols, and morespecifically, its role in retaining C and N in these soils.

Furthermore, examining the chemical reactivity of DOC can beuseful to understand its contribution to ecosystem dynamics(Weishaar et al., 2003). Over the past few decades, fluorescencespectroscopy has proven to be a fast and relatively inexpensivemethod for characterizing DOC. Three-dimensional excitation-emission matrices (EEMs), produced by the combination of emis-sion spectra with excitation wavelengths, can be used to producefluorescence indices and intensities (Fellman et al., 2010). Severalindices are used to determine different fluorescence characteristics.These include the fluorescence index (FI) which indicates whetherthe DOC is of terrestrial or microbial sources (Cory and Mcknight,2005; McKnight et al., 2001), the biological index (BIX) describedas “the index of recent autochthonous contribution” (p.716, Huguetet al., 2009), and the humification index (HIX), which measures theextent of humification (Zsolnay et al., 1999). Parallel factor (PAR-AFAC) analysis (Murphy et al., 2013) helps further characterize DOCcomposition (e.g. humic, protein-like, etc.) using data derived fromEEMs (Fellman et al., 2010).

Besides its contribution to soil physical and chemical properties,biochar offers an alternative way to reduce agricultural wastecompared to other organic amendments. Converting animal andcrop waste to biochar significantly reduces the volume and weightof the waste, and requires fewer applications than fertilizers whichneed to be applied annually (Lehmann and Joseph, 2009). However,as Joseph et al. (2010) notes, the effect of biochar on the soil is“biochar- and site-specific”. Thus in this study, a variety of agri-cultural wastes readily found in the region were transformed intobiochar pyrolized at different temperatures to identify the influ-ence of both feedstock and pyrolysis on the agroecological perfor-mance of biochar when applied to a Brazilian Arenosol. Theobjectives were to: 1) observe the effect of biochar type (feedstocksand temperatures of pyrolysis) on bulk leaching dynamics of DOCand NO3

�, and 2) examine fluorescence characteristics of DOCleached from soil-biochar mixtures using fluorescence spectros-copy to infer DOC reactivity and fate. The hypotheses were thateucalyptus biochars would retain DOC more than the other bio-chars since it would increase soil C levels due to its feedstock's highC/N ratio, while higher temperature biochars would reduce DOClosses particularly of humic DOC because of their greaterrecalcitrance.

2. Materials and methods

2.1. Soil collection and biochar production

Soils from the top 0e20 cm layer were collected from an agri-

cultural field located within the farm Fazenda �Agua Azul(15�13055.200S, 54�57043.400W) managed by the agribusiness GrupoBom Futuro,178 km northwest of the state capital of Cuiab�a inMatoGrosso, Brazil, an area within the Cerrado. The soil collected wasclassified as an Arenosol (FAO soil classification), with a sandytexture (91% sand, 4% silt, 5% clay). Carbon and nitrogen levels inthe soil were 0.7% C and 0.08% N as determined by elementalanalysis (628 Series CHN Analyzer, LECO Corp., St. Joseph, MI). Theaverage pHwater was 5.8 and average CEC was 5.3 cmolc kg�1, with abulk density of 1.6 g cm�3. Over the last 10 years, the crops sown onthe study site included soybean, sorghum, maize, and cotton, withthe latter two crops grown in rotation with soy for the last threeyears (Afonso Campos da Silva, Grupo Bom Futuro, personalcommunication, 2014). Twelve biochars were commercially

produced (SPPT Ltda., Mogi Morim, S~ao Paulo, Brazil) from fourfeedstock materials: cotton husks, eucalyptus sawmill residue,sugarcane filtercake, and swine manure, slow-pyrolysed at threetemperatures (400�, 500�, 600 �C). These were subsequentlycrushed and sieved to <2 mm in order to have similar biocharparticle sizes between the different feedstocks.

2.2. Experimental design

In a greenhouse located at the Federal University of Mato Grosso(UFMT), Cuiab�a campus, 9 L volume pots with one hole drilled atthe bottom were filled with 8 kg of a <2 mm-sieved Arenosol.Twelve biochars (4 biochar feedstocks x 3 temperatures of pyrol-ysis) were applied to pots at 5% soil dry weight, mixed and com-pacted by hand, making a total of 52 pots (12 biochars x 4 replicatesplus 4 unamended soil controls). A high biochar application rate(equivalent to 80 t ha�1) was used to ensure a biochar effect wasdetected. The pots were divided into 4 blocks, with each blockrunning north-south along a greenhouse bench, with a replicate ofeach treatment (biochar amended soil) plus a control (unamendedsoil) randomly assigned to locations within each block. Thegreenhouse temperature was controlled to 28 ± 2 �C, similar totemperatures during which the dry season maize is grown fromJanuary to June (INPE, 2012).

Water was initially added to achieve field capacity and allowedto equilibrate. Since fertilizer applications are a standard manage-ment practice in the region, fertilizer was added to the pots cor-responding to the amount each maize plant requires at the rate of150 kg NPK þ S, 150 kg KCl and 200 kg urea for 60,000 plants/hectare in the field (Afonso Campos da Silva, Grupo Bom Futuro,personal communication, 2014). Fertilizer, 2.5 g NPK þ S (12-46-0 þ 7), was added after 1 week and four maize seeds were plantedin each pot. Crushed KCl (2.5 g) and diluted urea (2.0 g in 50 mLwater) were added 20 days after planting, followed by a seconddiluted urea application of 1.3 g 7 days later. Watering thereaftertook place once a week then three times a week once the plantsbegan to grow, adding water at 110% field capacity each time toproduce sufficient leachate from each pot.

2.3. Laboratory analysis

Elemental analysis (C, H, N) of the 12 biochars was performed ona CHN Analyzer (628 Series, LECO Corp., St. Joseph, MI). Oxygencontent of the biochars was calculated as O¼ 100-(C þ Hþ Nþ ashcontent). Ash content was determined by placing 1 g of each bio-char in crucibles and heating in a muffle furnace to 900 �C for 4 h(Fuertes et al., 2010). Biochar pH was determined from 1:2.5 bio-char:water mixtures. Biochar extracts (i.e. without soil) were madeby mixing 3 g of each biochar into 30 mL of distilled water, heatingin an oven at 50 �C for 24 h, then centrifuging for 5min at 5000 rpmbefore filtering (Lin et al., 2012). Extracts were then analyzed forDOC characteristics. Biochar properties are presented in Table S1 inthe supplemental material. Additional physical properties (e.g.surface area, porosity, particle size) can be found in Speratti et al.(2017). Total C and N in soils post-experiment were also analyzedon a CHN Analyzer.

Leachate was collected once per week for 6 weeks and filteredthrough 0.7 mm glass fiber filters. DOC and NO3

� concentrationswere determined weekly immediately after collection using aUVeVis spectrophotometer (Spectrolyser; S-can, Austria) (Van DenBroeke et al., 2006). Since concentrations were higher than thespectrophotometer's range, samples were diluted with ultrapurewater. DOC fluorescence characteristics fromweekly samples wereanalyzed by obtaining EEMs on an Aqualog spectrofluorometer

A.B. Speratti et al. / Journal of Environmental Management 211 (2018) 256e268258

(Horiba Scientific, NJ, USA) as described by Eykelbosh et al. (2015).Briefly, samples were placed in a 10 mm quartz cuvette andanalyzed at an integration time of 1 s. The fluorescence EEMs ob-tained from the Aqualog were then used to determine the fluo-rescence index (FI) (McKnight et al., 2001), humification index(HIX) (Zsolnay et al., 1999), and biological index (BIX) (Huguet et al.,2009), as well as PARAFAC components (Murphy et al., 2013). DOCcharacteristics of biochar extracts were determined in the samemanner and are shown in Table S1 and Fig. S1.

The FI is derived from the ratio between emission (em) wave-lengths at 450 and 500 nm at excitation (ex) wavelength 370 nm(McKnight et al., 2001). The BIX is calculated as the ratio betweenemwavelengths at 380 nm (representing themaximum intensity ofthe b fluorophore) and 430 nm (representing the maximum in-tensity of the a fluorophore) at 310 nm excitation (Huguet et al.,2009). Lastly, the HIX is calculated as the peak area under em435e480 nm divided by em 300e445 nm, at ex 254 nm (Zsolnayet al., 1999).

2.4. Statistical analysis

The effects of biochar treatments including the control on DOCand NO3

� concentrations were determined by repeated measuresanalysis of variance (ANOVA) using IBM® SPSS® Statistics (Version23, SPSS. Inc., Chicago, USA), with “treatment” as the between-subjects factor and “time” as the within-subjects factor. Treat-ments were then separated by biochar feedstock and temperatureof pyrolysis and their effect on total DOC and NO3

� concentrationswas determined by multivariate ANOVA (MANOVA). Where dif-ferences were significant, a post-hoc Games-Howell test (P < .05)was used to compare means, as variances were unequal. Pearsoncorrelation coefficient and linear regression between DOC and NO3

�

were determined. Values presented in graphs and text aremeans ± 1 standard error (SE).

EEMS data was corrected for inner filter effects, dilution factors,and Raman scattering, before performing Raman normalisation, onR (version 3.3.1) using RStudio. Fluorescence indices (FI, HIX, andBIX) were also determined by R following calculations byMcKnightet al. (2001), Zsolnay et al. (1999), and Huguet et al. (2009) for eachindex, respectively, which was performed using the eemR packagefor R (Massicotte, 2016). PARAFAC modeling with non-negativity

Fig. 1. a)Mean dissolved organic carbon (DOC, mg L�1) and b) nitrate (NO3�, N mg L�1) per w

the effect of biochar treatment (Treat) on weekly (Time) DOC and NO3� measurements. A Gre

for lack of sphericity. Significant effects are indicated by ** (P < .01).

constraint was carried out using MATLAB (R2016a, The Math-Works Inc., USA) and the drEEM 0.1.0 and N-way 3.20 toolboxes, todetermine the number of components in the model following thetutorial by Murphy et al. (2013). Split-half analysis was used tovalidate the PARAFAC model (Murphy et al., 2013). The type offluorescence component and its probable source was thendescribed following Fellman et al. (2010). The fluorescence in-tensity at the maximum (Fmax) (Murphy et al., 2013) was alsodetermined by PARAFAC analysis for each component and sample.The effect of biochar treatments on fluorescence indices and onFmaxs over time were determined with repeated measures ANOVAon SPSS. Relative abundance (%) of Fmaxs was calculated as Fmax/SFmax (Murphy et al., 2013). Where differences between treat-ments were significant, but variances unequal, a post-hoc Games-Howell test (P < .05) was used to compare means. Pearson corre-lation coefficients and linear regressions were determined betweensoil C/N ratios and DOC and NO3

� concentrations with fluorescenceindices and Fmaxs. Principal component analysis (PCA) on DOC andNO3

� concentrations and DOC characteristics (FI, BIX, HIX, Fmaxs,and C/N ratio) in biochar treatments was carried out with theFactoMineR package (Le et al., 2008) in R (version 3.3.1).

3. Results

3.1. DOC and NO3� leaching varies among biochars

The repeatedmeasures ANOVA for DOC and NO3� concentrations

showed that there was a significant treatment, time, and time*-treatment effect (Fig. 1). Observing concentrations over time,leachate from cotton and swine manure biochars contained veryhigh levels of DOC and NO3

� in the first fewweeks, but leveled off bythe sixth week, whereas DOC and NO3

� in leachate from filtercakeand eucalyptus remained relatively stable and similar to the controlthroughout the 6 weeks (Fig. 1a and b). There was a slight increasein NO3

� concentrations in weeks 5 and 6 for all treatments exceptsoils with cotton biochar. This increase is likely related to the ureaapplications in weeks 4 and 5.

When the biochar treatments were separated by feedstock andtemperature of pyrolysis, the type of feedstock had a significanteffect on total DOC and NO3

� levels, while the temperature effectwas significant for some of the feedstocks (Fig. 2). For DOC levels,

eek per biochar feedstock and control, with results of the repeated measures ANOVA forenhouse-Geisser correction was applied for effect of time and its interaction to account

Fig. 2. a) Mean dissolved organic C (DOC, mg L�1) and b) nitrate (NO3�, mg L�1) per biochar feedstock and temperature of pyrolysis over 6 weeks (mean ± 1 SE). Capital letters

indicate significant differences between the feedstocks and control, and lowercase letters between temperatures for each feedstock (Games-Howell test; P < .05).

A.B. Speratti et al. / Journal of Environmental Management 211 (2018) 256e268 259

temperature differences were significant for each feedstock exceptcotton biochar (Fig. 2a). Leachate from soils with cotton biocharshad the greatest mean DOC (618.4 ± 65.7 mg L�1) over the exper-iment, followed by swine manure (190.8 ± 20.3 mg L�1), filtercake(51.9 ± 5.5 mg L�1) and eucalyptus (40.8 ± 2.2 mg L�1) biochars.Mean DOC values for filtercake and eucalyptus did not differ fromeach other nor were significantly greater than the control(44.6 ± 4.8 mg L�1) (Fig. 2a). Mean NO3

� had similar treatment ef-fects as DOC, with only swine manure biochar showing a differencebetween the temperatures (Fig. 2b). DOC and NO3

� concentrationsin leachatewere significantly (P< .05) correlated, with an R2 of 0.91.In addition, all biochars significantly (P < .05) increased total soil C(%) compared to the control, with filtercake biochars increasing soilC the least (Fig. 3a). All biochars, except for eucalyptus biochar, alsosignificantly increased total soil N (%) compared to the control(Fig. 3b). There were no differences between the temperatures foreither soil C or N.

3.2. DOC fluorescence indices

The repeated measures ANOVA for the fluorescence indices

Fig. 3. a) Mean soil total C (%) and b) total N (%) per biochar feedstock and temperaturefeedstocks and control (Games-Howell test; P < .05). There were no significant differences

showed a significant treatment, time, and time*treatment effect forall three indices (Fig. 4). Looking at changes over time, for both FIand BIX, almost all treatments including control experienced a peakin week 5 (Fig. 4a and b), similar to the increase observed in NO3

�

concentrations. However, neither was significantly correlated withNO3

� concentrations. FI was very poorly, but significantly, correlatedwith DOC concentrations (R ¼ 0.14; P < .05). For HIX, the oppositewas observed, with a decline in week 5 for most treatments(Fig. 4c). HIX was significantly, but also very poorly, correlated withNO3

� concentrations (R ¼ 0.14; P < .05), as well as with DOC con-centrations (R ¼ 0.17; P < .01). Although the correlations were notsignificant, higher soil C/N ratios tended to have low FI and BIXvalues and high HIX values (Fig. S2).

When looking at the biochar feedstocks and temperatures ofpyrolysis, cotton biochars had the lowest FIs, followed by euca-lyptus and swine manure biochars. Filtercake biochar had thehighest FIs and was the only biochar with FIs significantly higherthan the control (Fig. 5a). FIs decreased significantly (P < .05) astemperature of pyrolysis increased for all biochars, although the400 and 500 �C did not differ significantly for the eucalyptus andfiltercake biochars (Fig. 5a). For the BIX, cotton, eucalyptus and

of pyrolysis after 6 weeks. Capital letters indicate significant differences between thebetween the temperatures for each feedstock.

Fig. 4. Mean weekly a) fluorescence index (FI), b) biological index (BIX), and c) humification index (HIX) (no units) per biochar feedstock and temperature as well as control, withresults of the repeated measures ANOVA for the effect of biochar treatment (Treat) on weekly (Time) DOC characteristics. A Greenhouse-Geisser correction was applied for effect oftime and its interactions to account for lack of sphericity. Significant effects are indicated by * (P < .05) and ** (P < .01).

A.B. Speratti et al. / Journal of Environmental Management 211 (2018) 256e268260

Fig. 5. Mean a) fluorescence index (FI), b) biological index (BIX), and c) humification index (HIX) (no units) per biochar feedstock and temperature of pyrolysis after 6 weeks. Capitalletters indicate significant differences between the feedstocks and control, and lowercase letters indicate significant differences between temperatures for each feedstock (Games-Howell test; P < .05).

A.B. Speratti et al. / Journal of Environmental Management 211 (2018) 256e268 261

swine manure biochars were not significantly different from eachother, while filtercake biochar had the highest BIXs compared tothe other biochars and the control. The differences between tem-peratures of pyrolysis were similar as the FIs for cotton and swinemanure biochars, with BIX decreasingwith increasing temperature.The BIX for eucalyptus, however, did not differ between tempera-tures and for filtercake, the 400 �C temperature had higher meanBIX than the 600 �C, but was not higher than the 500 �C (Fig. 5b).For the HIX, cotton, swine manure, and filtercake biochars weresignificantly (P < .05) different from each other, but swine manurebiochar was not significantly different from eucalyptus biocharwhich did not differ from the control. Only cotton and swinemanure biochars had significantly higher HIX than the control. Thedifferences between the temperatures showed the opposite trendseen with the FI and BIX: the HIX increased with increasing tem-perature of pyrolysis. Although the HIX for the 500 and 600 �Ctemperatures did not always vary from each other (except for swinemanure), the HIX for the 400 �C was always lower than the 600 �Ctemperature (Fig. 5c).

3.3. EEMs PARAFAC analysis

Comparing models with 2- to 8-components through PARAFACanalysis of EEMs, a 5-component model was applied based on split-half validation and PARAFAC results of other biochar or soil DOCstudies (e.g. Uchimiya et al., 2013). Examples of EEMs for eachtreatment in our study are shown in Figs. S3 and S4, the spectralloadings and contour plots of the 5-component model in Fig. S5 inthe supplemental material.

Based on the PARAFAC analysis and following the review byFellman et al. (2010), the 5 components identified were: 1) UVChumic-like, 2) UVA humic-like, 3) UVC humic-like, 4) humic-like,

Table 1PARAFAC components identified following the review by Fellman et al. (2010).

Component Excitation (nm) Emission (nm) Source and descr

1) UVC humic-like 320e360 420e460 Terrestrial; high-2) UVA humic-like 290-325 (<250) 370e430 Likely derived fro3) UVC humic-like <250 (305) 412e416 Terrestrial; high m4) humic-like 250 550 Terrestrial or mic5) tryptophan-like 270-280 (<240) 330e368 Terrestrial, autoch

partially degrade

and 5) tryptophan-like, summarized in Table 1. The mean andstandard error of the Fmax (Raman units) of each component foreach treatment are shown in Table S2. Overall, components 1 and 2had higher mean Fmaxs compared to components 3, 4, and 5.

Separating the treatments by feedstock and temperature foreach component's Fmax (Fig. 6) showed that there were differencesbetween feedstocks and between temperatures of pyrolysis forsome feedstocks. For Fmax1 (UVC humic-like), cotton, swinemanure, and filtercake biochars were significantly (P < .05)different from the control and eucalyptus biochar. For swinemanure and filtercake feedstocks, the biochars pyrolysed at 400 �Chad higher Fmaxs than at 500 and 600 �C (Fig. 6a). For Fmax2 (UVAhumic-like), swine manure and filtercake feedstocks were signifi-cantly greater than the control and the other two feedstocks. Forcotton, swine manure and filtercake biochars, the 400 �C biocharshad the highest mean Fmaxs compared to the other temperatures,although it was not significantly different than the 500 �C biocharfor filtercake (Fig. 6b). For Fmax3 (UVC humic-like), all biocharfeedstocks were significantly different from each other (P < .05),but only cotton and swine manure biochars were different from thecontrol. Only swine manure and filtercake biochars had differencesbetween the temperatures, with the Fmax for 400 �C lower thanthat of 600 �C (Fig. 6c). For Fmax4 (humic-like), cotton and swinemanure biochars had significantly greater Fmaxs than the controland the other biochars. For cotton, the 400 �C biochar had signifi-cantly lower Fmax than the 500 �C, for swine manure 400 �C wassignificantly greater than the 500 �C, and for filtercake the 400 �Cwas significantly greater than the 600 �C (Fig. 6d). Lastly, for Fmax5(tryptophan-like), cotton, swine manure, and filtercake biochars allhad significantly greater Fmaxs than the control and eucalyptusbiochar. Between the temperatures, the swine manure 400 �Cbiochar was significantly greater than both the 500 and 600 �C, and

iption

molecular-weight humicm autochthonous production or microbial processing; low molecular weightolecular weight humic

robial sources; reduced humic-likethonous production, or microbial processing; may reflect intact protein or

d peptides

Fig. 6. Mean Fmax (Raman units) per biochar feedstock and temperature of pyrolysis for a) component 1 (Fmax1), b) component 2 (Fmax2), c) component 3 (Fmax3), d) component4 (Fmax4), and e) component 5 (Fmax5). Capital letters indicate significant differences between the feedstocks and control, and lowercase letters indicate significant differencesbetween temperatures for each feedstock (Games-Howell test; P <0.05).

Table 2Percent relative abundance (Fmax/SFmax) of each component Fmax for a PARAFAC5-component model for biochar treatments and control (mean ± 1 SE).

Biochar Fmax relative abundance (%)

1 2 3 4 5

Control 29.4 ± 0.9 19.5 ± 0.55 16.6 ± 0.8 17.5 ± 0.9 17.0 ± 2.1Cotton400 19.3 ± 0.6 13.4 ± 0.5 36.6 ± 1.3 16.9 ± 0.8 13.8 ± 1.4Cotton500 18.3 ± 0.6 4.4 ± 0.3 42.5 ± 1.2 24.7 ± 1.0 10.0 ± 1.0Cotton600 20.8 ± 0.3 3.1 ± 0.3 38.4 ± 0.6 30.0 ± 0.8 8.1 ± 0.8Swine400 24.2 ± 0.2 45.3 ± 2.2 4.4 ± 1.2 7.8 ± 1.0 18.3 ± 0.5Swine500 26.4 ± 0.4 12.0 ± 0.9 28.1 ± 0.7 21.6 ± 0.9 11.9 ± 1.1Swine600 27.3 ± 0.4 4.7 ± 0.4 31.5 ± 0.3 29.1 ± 0.8 7.4 ± 0.9Eucalyptus400 29.6 ± 0.4 19.9 ± 0.5 19.2 ± 0.6 16.3 ± 0.4 15.1 ± 0.9Eucalyptus500 29.0 ± 0.4 19.6 ± 0.8 20.5 ± 0.6 17.3 ± 0.5 13.6 ± 0.8Eucalyptus600 30.4 ± 0.7 16.8 ± 0.8 20.8 ± 0.7 18.8 ± 0.5 13.2 ± 1.5Filtercake400 23.3 ± 0.5 56.0 ± 0.7 0.8 ± 0.4 5.8 ± 0.2 14.1 ± 0.4Filtercake500 19.7 ± 0.7 58.2 ± 1.3 1.5 ± 0.3 6.2 ± 0.2 14.3 ± 0.4Filtercake600 21.9 ± 0.5 34.5 ± 0.8 13.5 ± 0.5 11.1 ± 0.3 19.1 ± 1.5

A.B. Speratti et al. / Journal of Environmental Management 211 (2018) 256e268262

the filtercake biochar followed the pattern 400 > 500 > 600 �C(Fig. 6e). None of the Fmaxs were correlated with DOC or NO3

�

concentrations.For the control, its fluorescence was mostly represented by

Component 1 (29%) compared to the other components. Compo-nent 3 was most abundant for cotton 400 (37%), 500 (43%), and

600 �C (38%) and swine manure 500 (28%) and 600 �C (32%) bio-chars, but for swine manure 400 �C biochar Component 2 wasgreatest (45%). The eucalyptus biochars were similar to the controlwith the Component 1 most abundant, while filtercake biocharshad Component 2 dominating. Component 4 was the second mostdominating for cotton biochars and swine manure 500 and 600 �Cbiochars, while Component 5 was also high for swine manure400 �C and the filtercake biochars (Table 2, Fig. S6).

3.4. Principal component analysis

The PCA on DOC and NO3� concentrations along with DOC

characteristics (fluorescence indices and PARAFAC components)showed several groupings for each of the four biochar feedstocks(Fig. 7). Cotton biochars had three groupings: FI, BIX, Fmax2, andFmax5 (Group 1), Fmax1 and Fmax3 (Group 2), and Fmax4, DOCconcentration, NO3

� concentration, C/N ratio, and HIX (Group 3).The cotton biochars at 400 �C clustered near Group 1, while the500 �C biochars clustered closer to Group 2 and the 600 �C biocharsto Group 3 (Fig. 7a). For the swine manure biochars, the PCAshowed three groupings: Fmax4, Fmax3, and NO3

� concentration(Group 1), BIX and FI (Group 2), and DOC concentration, C/N ratio,Fmax1, Fmax2, Fmax5, and HIX (Group 3). Swine manure biocharsat 400 �C clustered closely to Group 2, the 500 �C biochars to Group

Fig. 7. Principal component analysis (PCA) of DOC and NO3� concentrations and DOC characteristics from soils with 12 biochars (4 feedstocks x 3 temperatures of pyrolysis).

A.B. Speratti et al. / Journal of Environmental Management 211 (2018) 256e268 263

1, and the 600 �C biochars to Group 3 (Fig. 7b). For eucalyptusbiochars, two groupings stood out: HIX, DOC and NO3

� concentra-tions, and C/N ratio (Group 1), and Fmax1, Fmax2, Fmax3, Fmax4,Fmax5, FI, and BIX (Group 2). Eucalyptus biochars at 400 �C and500 �C clustered closely to Group 1, while the 600 �C biocharsclustered by Group 2 (Fig. 7c). Lastly, the PCA for filtercake biocharsshowed two main groupings: Fmax3 and DOC concentrations(Group 1) and BIX, FI, NO3

� concentrations, C/N ratios, Fmax1,Fmax2, Fmax3, Fmax4, Fmax5, and HIX (Group 2). Filtercake bio-chars at 400 �C clustered closely to Group 2, while the 500 �C and600 �C biochars clustered closer to Group 1 (Fig. 7d).

4. Discussion

4.1. DOC and nitrate leaching

Cotton and swine manure biochars led to much higher DOClosses in soil leachate compared to the control soils at the initialtime of application. During biochar pyrolysis, low-molecular-weight organic compounds are produced that are labile or leach-able, and some can adsorb to the biochar surface (Lin et al., 2012).The high losses from cotton and swine manure biochar treatmentsafter initial application are likely derived from the more labilepolysaccharide organic matter of the biochars which do not adsorbas well and are flushed into the DOM (Kaiser and Guggenberger,2000). Barnes et al. (2014) observed a similar effect when biochar

was added to sandy soils with low organic matter, suggesting thatthe C source in DOC losses was mostly biochar-derived, and notfrom the soil itself. As in our study, DOC losses from biochar-amended soils in Barnes et al. (2014) decreased over time,implying that the more labile biochar-C was rapidly depleted.

In contrast to the cotton and swine manure biochars, eucalyptusand filtercake biochars did not have drastically higher initial peaksin DOC leaching, but rather remained relatively stable throughoutthe six weeks. This suggests that the eucalyptus and filtercakefeedstocks have less labile or leachable C than the cotton and swinemanure feedstocks. Similarly, Eykelbosh et al. (2015) observed thatsugarcane filtercake biochar decreased DOC export in a 4-monthcolumn experiment and that the leached DOC consisted mostly oflabile components. Cotton biochar and eucalyptus biochar had highlevels of C compared to the other biochars for all pyrolysis tem-peratures (Table S1), but C from cotton biochar appears to havebeen more labile. This is probably due to the high lignin content ineucalyptus, which ranges between 23% and 34% (Rodrigues et al.,1998), compared to lower lignin content in cotton, around 15%(Ververis et al., 2004). Sugarcane filtercake, similar to eucalyptus,has a relatively high lignin content which can be around 32%(Eykelbosh et al., 2014). Animal manures typically contain lowerlignin contents (Brown et al., 2015), noting that pig feed in Brazilmostly consists of cereals such as low-lignin contentmaize and rice,and legumes such as soybean (EMBRAPA, 2003), thus containingmore labile C from cellulose and hemicellulose than woody

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feedstocks or sugarcane.H/C and O/C ratios are often used as measures of aromaticity

levels in biochar, with higher H/C and O/C ratios observed for low-temperature biochars (Krull et al., 2009). This was the case for ourbiochars where the H/C and O/C ratios were higher for the 400 �Cbiochars compared to the 500 and 600 �C biochars (Table S1). LowH/C and O/C ratios imply higher aromaticity and stability (Keiluweitet al., 2010; Van Zwieten et al., 2010). As temperature of pyrolysisincreases, aromatic C in biochars increases, with biochars producedat temperatures �400 �C containing less than 10% non-aromatic C(Kleber et al., 2015). Differences between temperatures of pyrolysiswere observed for DOC leached from soils with swine manure,eucalyptus, and filtercake biochars (Fig. 2a). The biochars at 400 �Chad significantly greater DOC losses than the higher temperaturesfor swine manure and filtercake feedstocks, but not for eucalyptus.The higher non-aromatic fraction in low-temperature biochars maymake them more accessible for microbial activities, e.g. decompo-sition, compared to high-temperature biochars (Joseph et al., 2010).

Cotton and swine manure biochars, particularly at lower tem-peratures as noted for swine manure biochar, may have stimulatedmicrobial activity and SOM decomposition more, leading to higherDOC leaching than the other biochar feedstocks. Yet, biocharamendment can also decrease soil respiration and thus SOMdecomposition (Eykelbosh et al., 2015; Jones et al., 2011; Keith et al.,2011), which may have occurred in eucalyptus and filtercake bio-char treatments. DOC concentrations in leachate lowered over thecourse of the experiment (Fig. 1a), suggesting that microbial ac-tivity stabilized as the biochar-soil mixtures aged. These resultsimply that feedstock played a greater role in retaining DOC in thesoil compared to pyrolysis temperature.

Similar to their DOC losses, cotton and swine manure biocharscontributed to higher NO3

� losses in their leachate compared to thecontrol and the other two biochars. Manure-based biochars oftenhave high total N content because of the high protein content oftheir feedstock. Plant-based biochars in turn usually have less N,but higher C content (Ippolito et al., 2015). Both cotton and euca-lyptus biochars had high total C, but unlike eucalyptus biochar,cotton biochar had high total N similar to swine manure biocharand greater than filtercake biochar (Table S1). However, available Nin biochars in the form of NO3

� has been reported in the literature tobe mostly negligible (Ippolito et al., 2015). Thus, cotton and swinemanure biochars likely led to release of N from the soil as NO3

�

while eucalyptus and filtercake biochars retained NO3� in the soil,

though not significantly more than the control.Our results are in contrast to other studies, such as Uzoma et al.

(2011) who observed that black locust biochar significantlyretained NO3

� in sandy soils compared to the control over time.Zheng et al. (2013) also found that giant reed biochar reduced NO3

�

leaching after N fertilizer application. Biochar has the potential toadsorb ammonia (NH3), as well as retain ammonium (NH4

þ) byincreasing CEC, thus reducing nitrification and preventing NO3

�

leaching (Clough and Condron, 2010).The high initial NO3

� losses in our study are likely due to the NPKfertilizer application in the first week, and the increase in weeks 5and 6 to the urea applications in weeks 4 and 5, as the recent Ninputs may have stimulated microbial activity. The differences be-tween the biochar treatments, however, may be related toincreased nitrification in the soils, with cotton and swine manurebiochars causing more nitrification than the other biochars.Eykelbosh et al. (2015) also noted increased NO3

� leaching in fil-tercake biochar-amended soils, suggesting the biochar may haveincreased mineralization of soil organic N by improving soilporosity and aeration.

Nitrification in soils is related to NH4þ availability; if NH4

þ

adsorbed to biochar remains available, soil NO3� levels, and

presumably leaching, would increase in soils with biochars (Thieset al., 2015). Dempster et al. (2012) observed a significantlyreduced inorganic N pool in soils with Jarrah wood (Eucalyptus sp.)biochar, as well as decreased nitrification rate with increasingbiochar application rate in all three N treatments (organic N, inor-ganic N, and basal N additions). The authors suggested the reducednitrification rate in the presence of biochar was due to lower NH4

þ

levels caused by substrate limitation; biochar had a negative effecton SOM decomposition as well. The opposite may have occurred inour study: cotton and swine manure biochars provided additionalmicrobial substrate, contributing to increased NH4

þ levels in thesoils and increasing nitrifying activity and NO3

� production. In fact,Yoo and Kang (2012) found that swine manure biochar increasednet N mineralization and net nitrification in silt loam soils in alaboratory incubation study, stating a need for caution when usinghigh N biochars as soil amendments. Eucalyptus and filtercakebiochar, in contrast, may not have contributed as much to NH4

þ

levels in the soil. Although biochars with high C/N ratio (>30) cancause lower N mineralization, this can be overcome by adding Nfertilizer (Jeffery et al., 2015), as was done in the present study. Inaddition, cotton biochar (with a high C/N ratio) and filtercake bio-char (with a low C/N ratio) had the opposite effects on NO3

�

leaching, and NO3� concentrations were not significantly correlated

with soil C/N ratios. Other mechanisms that may have affectedhigher NO3

� losses in cotton and swine manure biochar treatmentsare increased hydraulic conductivity (Kameyama et al., 2012) andincreased negative charge density (Liang et al., 2006) in soilsamended with these biochars.

4.2. DOC characteristics

Along with DOC concentrations, DOC characteristics in eachbiochar treatment's leachate were examined using three indicesdetermined by fluorescence spectroscopy (FI, BIX, and HIX) andPARAFAC analysis.

4.2.1. Fluorescence indexLow FI ratios (~1.4) indicate DOC primarily derived from

terrestrial sources such as plants and soil organic matter, whilehigher FIs (~1.9) indicate DOC from microbial sources (McKnightet al., 2001). Over time, FI decreased for most treatments(Fig. 4a), indicating that DOC derived from microbial sourcesdecreased as microbial activity slowed down. At week 5, however,DOC from all biochars experienced an increase in FI suggesting anincrease in microbial activity. Although there was no significantcorrelation betweenmean FIs and NO3

�, the FI peaks may be relatedto the NO3

� increases also observed in week 5 following urea ad-ditions the week before, which may have stimulated microbialactivity. Despite DOC and NO3

� being highly correlated in our study,and evidence of a strong link between the C and N cycles (Grant,1995), no relationship between FI (or other DOM characteristics)and NO3

� was found, as was the case for Tye and Lapworth (2016).The FI was also overall independent of DOC concentrations in ourexperiment, as noted in other studies (e.g. Jaff�e et al., 2008; Tye andLapworth, 2016).

In our study, all treatments had mean FIs between 1.2 and 1.4except for swine manure biochar at 400 �C (1.7 ± 0.04), and filter-cake biochar at 400 (1.8± 0.01) and 500 �C (1.8 ± 0.02) (Fig. 5a). Thissuggests that DOC from all biochar treatments was mainly derivedfrom terrestrial sources, but DOC from swine manure at 400 �C andfiltercake at 400 and 500 �C had more microbial sources than theother biochar treatments. Differences between the feedstocks forthe biochar-soil treatments (Fig. 5a) were similar to those betweenthe feedstocks for the extracts from biochar without soil (Fig. S1).

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However, FI values for cotton and filtercake biochar extracts weregreater at higher temperatures, whereas mixed with soil, the effectwas the opposite and FI values lowered for filtercake in particular.High FI values, which indicate more microbially-sourced DOC, aredue to a decline in emission with increasing wavelengths in sam-ples with microbial DOC (McKnight et al., 2001), while for terres-trial DOC, emission intensity increases with increasingwavelengths. DOC derived from terrestrial sources usually containsmore lignin than microbially-derived DOC (Fellman et al., 2009);thus a higher FI at a low temperature of pyrolysis would beconsistent for swine manure biochar. In contrast, filtercake has arelatively high lignin content (Eykelbosh et al., 2014) which doesnot explain the high FI for DOC from our treatments with filtercakebiochars at 400 and 500 �C. Fresh filtercake additions, however, canstimulate soil microbial activity and respiration (Rasul and Khan,2008). The filtercake biochars at 400 and 500 �C may thereforestill have contained enough bioavailable C to contribute to soilmicrobial activity compared to filtercake biochar at 600 �C, sincenon-labile C fractions increase with increasing temperature of py-rolysis (Nelissen et al., 2012). Similarly, in a study comparing DOMfrom different soil types, Tye and Lapworth (2016) noted throughprincipal component analysis that the DOM from the soils wasmostly terrestrially derived, and that the labile components werelikely related to microbial activity. In addition, although not sig-nificant, FI values in our study tended to increase with lower soil C/N ratios, suggesting that biochar treatments with low soil C/N ratioshad DOC derived from mostly microbial, rather than terrestrial,biomass (Jaff�e et al., 2008). Both filtercake and swine manure bio-chars had relatively low C/N ratios compared to cotton and euca-lyptus biochars (Table S1).

4.2.2. Biological indexSimilar to the freshness index (b/a) (Parlanti et al., 2000), the b

fluorophore is related to autochthonous and fresh DOMwhile the afluorophore is associated with older, more degraded material.Higher ratios (>1) represent more recently produced DOM of bio-logical origin, while lower ratios (0.6e0.7) correspond to morehumified, less biological material (Birdwell and Valsaraj, 2010;Huguet et al., 2009). The BIX in our study varied significantlyover time, in general lowering in the first few weeks with a peakoccurring for most treatments in week 5 (Fig. 4b). Organic materialin the treatments was thus decomposing in the first few weeksbefore a nutrient input (e.g. urea) caused an increase in microbialactivity resulting in the release of more autochthonous, fresh DOC.In our study, cotton, swinemanure, and eucalyptus biochars did notdiffer significantly from each other or from the control; only fil-tercake biochar had significantly greater BIX than the other treat-ments (Fig. 5b). This was similar to the BIX of the extracts frombiochar (i.e. without soil), although the BIX for cotton biochar ex-tracts was greater at higher temperatures (Fig. S1), in contrast totheir BIX when mixed in soil. The high BIX of the filtercake biochartreatments suggests that the DOC leached from them was fresherthan that lost from the other biochar treatments. Swine manurebiochar at 400 �C also had similar BIX as the filtercake biochars atthe lower temperatures, a similar trend as with their FIs. Althoughnot significantly correlated, treatments with lower soil C/N ratiohad higher BIX values (Fig. S2), indicating DOC from those treat-ments was fresher. Not surprisingly, for most treatments, the BIXdecreased with increasing temperature of pyrolysis, as biocharbecomes more resistant to decomposition at higher temperatures(Kleber et al., 2015).

4.2.3. Humification indexHigh HIX ratios indicate higher humified organic material and

thus the presence of more complex, aromatic molecules (Huguetet al., 2009). Low ratios (<10) indicate relatively non-humifiedDOM coming from biomass; as biomass decomposes, HIX ratioswill increase (Birdwell and Valsaraj, 2010). The HIX in our experi-ment varied considerably over time, increasing in the first twoweeks, then dropping either gradually or dramatically for sometreatments until the lowest point at week 5 (Fig. 4c). The HIX forcotton biochar at 400 and 500 �C, however, increased fromweek 3before gradually dropping towards the end of the experiment atweek 6. DOM in most treatments thus began as less humified,indicating microbial activity, followed by more humified asdecomposition progressed and slowed down, and then experienceda burst of microbial activity (again possibly due to urea applica-tions) which once again lowered humification rate. This variationover time is not unusual as DOM quantity and quality are known tovary spatially and temporally in relation to its source material andenvironment (Hansen et al., 2016). Birdwell and Valsaraj (2010)observed that DOM in fogwater samples changed significantlyfrom more humified (HIX 6.4) and terrestrially sourced (FI 1.4, BIX0.6) to less humified (HIX 3.9) and biologically sourced (FI 1.8, BIX0.1) in only a 4 h period. As with the FI and BIX for our treatments,the HIXwas not significantly correlatedwith the soil C/N ratio, but atrend was noticeable of higher HIX with higher soil C/N ratio.

HIX values from soils can range from 10 to 30 (Birdwell andEngel, 2010). In our study, HIX values ranged from as low as 4.3(swine manure biochar at 400 �C) to as high as 17.5 (swine manurebiochar at 600 �C). Cotton and swine manure biochar treatmentshad high HIX values compared to the other biochar feedstocks,while eucalyptus and filtercake biochar treatments were similar tothe control (Fig. 5c). In contrast, the HIX values for the biocharextracts without soil (i.e. “biochar only”) were highest for cottonbiochars, and not as high for swine manure biochars. As the HIX forthe cotton biochar only extracts were similar to those of the cottonbiochar-soil treatments, DOC from these treatments may havederived mostly from the biochars themselves. The HIX for swinemanure, eucalyptus and filtercake biochar treatments were higherthan the HIX of their biochar only extracts (Fig. S1), implying thatsoil DOCwas also lost, but themuch higher HIX from swinemanurebiochar treatments suggest these biochars in particular led to highsoil DOC losses (Fig. 5c). Swine manure biochar at 400 �C and fil-tercake at 400 and 500 �C had low HIX values, consistent with theirhigh FI and BIX values and observed in their biochar only extracts,meaning they contained less humified DOM from microbial ratherthan terrestrial sources. The HIX values for eucalyptus biochartreatments were around 10 and lower, suggesting that DOC leachedfrom these treatments was slightly humified for the higher tem-perature biochars and less humified for the lower 400 �C biochar.

4.2.4. PARAFAC analysisThe PARAFAC components for DOC identified in our study, based

on Fellman et al. (2010), coincided with the fluorescence indices forthe different treatments described above. Component 3 wasgreatest for cotton biochar treatments and swinemanure biochar at500 and 600 �C. This is consistent with their low FI and BIX andhigh HIX values. Component 3 has been characterized as bothoxidized quinone-like (Ishii and Boyer, 2012) and as reduced qui-nones that are more aromatic than oxidized quinones (Cory andMcknight, 2005). The Component 3 identified by Uchimiya et al.(2013) with 250/470, 350/470 peaks was also UVC humic-like anddecreased with increasing temperature of pyrolysis, whileComponent 3 in our study appeared to either remain the same orincrease with temperature (Table 2).

Filtercake biochars and swine manure biochar at 400 �C hadhigh Fmaxs for Component 2, consistent with their high FI and BIXand low HIX. The relative abundance of Component 2 lowered with

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increasing temperature of pyrolysis for all biochar feedstocks(Table 2). Other authors (Lin et al., 2012; Uchimiya et al., 2013) havelikewise noted that contributions of Component 2 humic-likefraction decreased with increasing temperature as the humicsfraction (humic and fulvic acid) was reduced. In addition, beingUVA humic-like, Component 2 is susceptible to photodegradationfrom UVA light (Ishii and Boyer, 2012).

Eucalyptus biochar treatments and the control were dominatedby Component 1, corresponding to their low FI and BIX, but notwith their low HIX. Component 1 represents more oxidized fluo-rophores (Cory andMcknight, 2005), but here, the lowHIX suggeststhe DOC was not humified. As DOC from eucalyptus biochartreatments was not much different from DOC from the controltreatment, eucalyptus biochar probably did not contribute much tolabile or leachable C, but may have prevented humified soil C fromleaching.

Component 4 was the next most highly represented componentfor cotton biochars and swine manure 500 and 600 �C biochars.This component increased with rising temperature of pyrolysis formost biochars, consistent with Uchimiya et al. (2013) who sug-gested the increase was due to the higher low-molecular weightacids fraction (Lin et al., 2012).

Component 5 was the only protein-like component, and it washigh for swine manure 400 �C and the filtercake biochars. Tye andLapworth (2016) also identified a tyrosine-like protein componentfrom soil DOM which was suggested to represent a more labileDOM fraction of microbial or plant cell sources. This is againconsistent with swine manure 400 �C and the filtercake biochartreatments’ high FI and BIX values and low HIX values. Swinemanure and filtercake biochars themselves also had high total Ncontent (Table S1), indicating they could contribute to proteins inthe labile DOC. In contrast to the swine manure biochar in ourstudy, Uchimiya et al. (2013) observed that poultry manure biocharhad very little contribution from protein-like Component 5. How-ever, the authors observed a decrease in Component 5 withincreasing temperature of pyrolysis similar to that observed in ourstudy. Component 5 was higher for biochars at 400 �C compared toat 600 �C for all biochar treatments in our study, except for filter-cake biochar where it was highest at 600 �C (Table 2). Component 5may be related to lignin content, with biochar feedstocks withhigher lignin content having a higher Component 5 contribution(Uchimiya et al., 2013). This would not explain the high Component5 contribution in the swinemanure 400 �C biochar which would beexpected to have a low lignin content, but it may explain the highComponent 5 for filtercake 600 �C. Similarly, another study withsugarcane filtercake biochar showed that the biochar retainedmore high-molecular weight, humic DOC species in the soil whilethe labile components were leached (Eykelbosh et al., 2015). Theauthors suggested that the filtercake biochar may have assisted inretaining humified components already existent in the soil.

4.3. Principle component analysis of DOC quantity and quality, aswell as NO3

� concentrations

PCA of DOC and NO3� concentrations and DOC characteristics

from the different biochar treatments supported the results dis-cussed above. Cotton biochar at 400 �C was clustered near Group 1(FI, BIX, Fmax5, and Fmax2) whose values were negatively corre-lated, indicating that DOC from the lower temperature cottonbiochar was more labile and of microbial sources compared to thehigher temperature biochars. In contrast, cotton biochars at 500 �Cand 600 �C clustered closer to Groups 2 and 3 whose variables werepositively correlated, suggesting DOC and NO3

� concentrations inleachate increased with increasing soil C/N ratio and UVC humic-like and humic-like components (Fmaxs 1, 3 and 4) (Fig. 7a). For

swine manure biochars, the 400 �C biochar was similarly clusterednear the negatively correlated Group 2 (FI and BIX), reinforcing itsprimarily microbial sourced DOC. Swinemanure at 500 �Cwas nearthe negatively correlated Fmax4 and Fmax3 indicating its DOC wasmore humic-like, while swine manure at 600 �C was clustered nearC/N ratio, HIX, Fmax1, Fmax 2, and Fmax 5 which were positivelycorrelated (Fig. 7b). This suggests that the DOC from the highertemperature swine manure biochar was mostly humic with someprotein and of terrestrial sources perhaps due to a higher lignincontent compared to the lower temperature biochars.

Eucalyptus biochars at 400 �C and 500 �Cwere closer to Group 1,with HIX, DOC, and NO3

� concentrations negatively correlatedmeaning that DOC and NO3

� concentrations in eucalyptus biocharleachates decreased with less humified DOC. Thus DOC leachedwasmostly of microbial source rather than terrestrial, implying soilDOCwas retained. Eucalyptus biochar at 600 �Cwas closer to Group2 whose variables were all positively correlated, suggesting thatDOC sources from this biochar were a mix of microbial andterrestrial (Fig. 7c). Lastly, filtercake biochar at 400 �C was clusteredby Group 2 whose variables were also positively correlated, exceptfor the HIX which was negatively correlated. As with the other400 �C biochars (except for eucalyptus), the positive correlationbetween FI and BIX suggest an increase in more labile DOC withmore biological, autochthonous DOCwhichwould be related to lesshumified DOC (lower HIX ratios). Tye and Lapworth (2016) alsoobserved a positive correlation between FI and b/a ratio with astrong negative correlation with HIX. The negative correlation withC/N ratio reemphasizes that DOC from filtercake biochar at 400 �Cwas more labile since, as previously mentioned, higher lignin bio-chars may contribute to more protein-like (Component 5) thanhumic-like DOC (Uchimiya et al., 2013). Filtercake biochars at500 �C and 600 �C were grouped by Fmax3 and DOC concentra-tions, suggesting that DOC concentrations from these biocharsincreased with terrestrially-sourced DOC more than microbial-sourced (Fig. 7d).

In addition to retaining DOC and NO3� in the soil, eucalyptus and

in particular filtercake biochars contributed to several soil chemicaland physical properties (e.g. higher Ca/Mg ratio, lower pH, largersand aggregate sizes) that appeared to improve soil structure andlikely contributing to higher maize biomass compared to the cottonand swine manure biochar treatments (Speratti et al., 2017).Further, PCA of the soil properties measured in Speratti et al. (2017)found that both biochar feedstocks had positive correlations be-tween Ca, Fe, andMn (Fig. S7). Metals such as Fe andMn, alongwithlower soil pH, can contribute to the formation of organo-mineraland/or organo-metallic associations that decrease biochar miner-alization. This can increase biochar-C stability in the soil whichmayimprove soil structure (Fang et al., 2013). Improved soil structuremay have influenced the higher terrestrial DOC and NO3

� retentionin filtercake and eucalyptus biochar treatments compared to cottonand swine manure biochar treatments.

5. Conclusions

The agricultural waste-derived biochars used in this studycontributed to both differences in DOC and NO3

� concentrations insoil leachate, and to differences in the optical and fluorescencecharacteristics of DOC in leachate. These DOC characteristics werefound to vary by feedstock and temperature of pyrolysis. ObservingDOC concentrations leached from each treatment and the quality ofthe DOC, it is clear that certain feedstocks contributed to the loss offresher DOC, while other feedstocks were associated with theleaching of more humified DOC. As hypothesized, eucalyptus bio-char treatments had very low DOC losses similar to the control, asdid filtercake biochar treatments particularly at 600 �C, with DOC

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that was leached from the biochar-soil mixtures primarily exhib-iting more labile, microbial-derived characteristics. Both feedstocksmay have contributed to stabilizing more humified C componentsin the soil compared to the other two feedstocks. Treatments withswine manure biochar (especially at 400 �C) lost higher amounts ofDOC than the control, mostly from microbial sources, but also hu-mified and terrestrially-derived DOC from higher temperaturebiochars. Similarly, treatments with cotton biochar lost the highestamounts of DOC, which was mostly of humified and terrestrialorigin. This, along with the high NO3

� levels in its leachate, givereason to believe that cotton biochar would not help preventnutrient leaching or stabilize C pools in an Arenosol, at least duringthe initial 6 weeks following application. Information from fluo-rescence spectroscopy with EEMs coupled with PARAFAC analysiscan assist in determining the right feedstock and temperature ofpyrolysis to produce a biochar suitable for the needs of producers(e.g. high FI and BIX, low HIX, such as for filtercake biochars). Of thefour agricultural residues analyzed, filtercake and eucalyptusshowed the most promise for retaining DOC and NO3

� in a BrazilianCerrado Arenosol when transformed into biochar, but combina-tions of biochars (e.g. cotton with filtercake or swine manure witheucalyptus) may produce additional benefits and remain to betested.

Acknowledgments

This work was supported by the Canadian Natural Sciences andEngineering Research Council (NSERC) Post-Graduate ScholarshipAward and an NSERC-Create TerreWEB Scholarship to ABS, theBelmont Forum and the G8 Research Councils Freshwater SecurityGrant [G8PJ-437376- 2012] through NSERC to MSJ, and a BrazilianNational Council for Scientific and Technological Development(CNPq) grant to EGC. The authors are grateful for the assistance ofG.N. Torres, E. Queiroz, A. Espinoza, A. Oliveira, and V.M. Soares inthe greenhouse. Special thanks to F. Lobo and C.E.R. Ortiz for lab-oratory space and to A. C. da Silva from Grupo Bom Futuro.

Appendix A. Supplementary data

Supplementary data related to this article can be found athttps://doi.org/10.1016/j.jenvman.2017.12.052.

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